pep8 changes to rigify (minor warnings still there)

also found quite a few cases where variables were used that hadnt been defined.

release/scripts/modules/rigify_utils.py

@@ -174,7 +174,6 @@ def blend_bone_list(obj, apply_bones, from_bones, to_bones, target_bone=None, ta
         blend_transforms(new_pbone, from_bone_name, to_bone_name)
 
 
-
 def add_pole_target_bone(obj, base_bone_name, name, mode='CROSS'):
     '''
     Does not actually create a poll target, just the bone to use as a poll target
@@ -320,10 +319,11 @@ def bone_class_instance(obj, slots, name="BoneContainer"):
     there are also utility functions for manipulating all members.
     '''
 
+    attr_names = tuple(slots) # dont modify the original
+
     if len(slots) != len(set(slots)):
         raise Exception("duplicate entries found %s" % attr_names)
 
-    attr_names = tuple(slots) # dont modify the original
     slots = list(slots) # dont modify the original
     for i in range(len(slots)):
         member = slots[i]